According to a report released by the Lawrence Berkeley National Laboratory, titled "The Treatment of Renewable Energy Certificates, Emissions Allowances, and Green Power Programs in State Renewables Portfolio Standards," states that have adopted renewable portfolio standards (RPS) have decided to use unbundled renewable energy certificates (RECs) to track RPS compliance. However, the report finds that greater clarity should be sought in areas associated with RECs.

The study examines legislation and regulatory rules from each of the 22 RPS policies currently in place in the U.S., with a particular emphasis on issues associated with RECs. The report evaluates how states treat air emissions reduction credits or emissions allowances under RPS policies - if those allowances are available to renewable generators. Although several states have been explicit about this issue (reaching different conclusions), most states do not directly and clearly address the question, which is becoming increasingly important as states adopt emissions cap-and-trade programs, the lab says.

"It's evident that certificate tracking systems increase the confidence of legislators and regulators when it comes to allowing RECs to be traded separately from electricity," says Edward Holt, a co-author of the report. "Even so, states have a wide variety of REC definitions and rules, and these rules are not always precise. Clarifying definitions would help remove uncertainty in the market and would benefit the renewable energy industry and consumers."